A typical transmissive type overhead projector, generally indicated as 10, is depicted in FIG. 1 and includes a base 12, a projection head 14 and a post 16 connecting the base 12 and the projection head 14. The post 16 is pivotable between the illustrated upright projection position and a storage position wherein the post 16 is rotated forward and down to engage a clip 18. The post 16 includes a collar 20 which may be slid relative to the post 16 to engage a tang (not shown in FIG. 1) attached to the base 12 when the post 16 is in the upright, projection position. The user of the projector 10 is required to lift the collar 20 from engagement with the tang when it is desired to move the post 16 to the storage position and push the collar 20 down into engagement with the tang after the post 16 has been moved to the projection position to maintain the post 16 in this projection position.
It has been found that the collar 20 has not been used regularly in the past, resulting in instability and possible incorrect positioning of the post 16 and it is desired to provide a collar which is automatic in its use so that the post 16 will be reliably and securely positioned in the upright position.